1. Field of the Invention
This invention relates in general to magnetic transducers for reading information signals from a magnetic medium and, in particular, to an improved magnetoresistive read transducer.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magnetoresistive material as a function of the amount and direction of magnetic flux being sensed by the element.
In the past, principal problems with the MR sensors of unstable operating characteristics and Barkhausen noise have limited their use. These problems arise because there generally exist more than one stable state for the magnetization, a degeneracy which typically produces various multi-domain configurations. Random changes in this configuration are the cause of the above-mentioned unstable operating characteristics and Barkhausen noise.
The conceptual solution to these prior art problems was attained only recently through the implementation of patterned longitudinal bias. This solution is described and claimed in the commonly assigned patent application entitled Magnetoresistive Read Transducers by Ching H. Tsang, Ser. No. 766,157, filed 8-15-85 U.S. Pat. No. 4,663,685. Briefly, this invention advocates the creation of appropriate single domain states directly in the end regions only of the MR layer. This can be achieved by producing a longitudinal bias in the end regions only of the MR layer to maintain the end regions in a single domain state and these single domain states induce a single domain state in the central region of the MR layer. In a specific embodiment of this concept, a thin film of soft magnetic material is provided parallel to, but spaced from, the MR layer to also produce a transverse bias in the central region only of the MR layer to maintain the central region, where the output signal is sensed, in a linear response mode.
The introduction of the soft magnetic material, in the above-discussed specific embodiment, however, may create additional magnetic issues. Specifically, as this embodiment induces a single domain state only in the end regions of the MR layer but leaves the domain state in the end regions of the soft magnetic bias film undefined the total amount of magnetic flux coming in from the passive end regions is still undefined and some unstable operating characteristics and Barkhausen noise may still occur.